This invention relates to a rolling bearing having rolling elements equidistantly spaced about the bearing circumference. The rolling elements are held in place relative to each other by a retainer. The rolling elements and their retainer are positioned about inner and outer races. Grease seals in the form of seal plates or webs are secured at the ends of the bearing to the outer race to retain the grease used to reduce the friction between the rolling elements, retainer and races as the bearing rotates. The rolling bearing will be referred to herein as a roller bearing for convenience sake.
Grease seals are commonly employed in roller bearings used in various mechanisms and tools. Grease leaks and short lubricant life are problems often encountered with such rolling bearings, particularly when they are subjected to a high temperature and high speed operation. For instance, the bearing assembly for an electromagnetic clutch used in a car cooler compressor is known to be susceptible to grease leaks, with the grease escaping past the grease seal. It has been proposed, in an effort to prevent grease leaks, to provide a bearing assembly which incorporates therein a contact seal with the end of the outer race located closest to the electromagnetic clutch and a non-contact seal with the end of the outer race located closest to the compressor. Such an arrangement is described in Japanese Patent Publication No. 26269/78.
A generally known and available electromagnetic clutch of this type is illustrated in FIGS. 1 and 2. It is fabricated so that rolling bearing 3 is arranged on a boss 2 formed in a clutch body 1. A rotor includes a disc 5 disposed to face but be in non-contact with the front of an electromagnet 4 secured to the body 1. A cylindrical portion 6 axially extends from the inner periphery of the disc 5 over the generally cylindrical outer race 12 of the ball bearing 3. V belts 8, which are adapted to transmit torque from a drive source, are fitted on a pulley 7 integrally formed with the outer periphery of the disc. In FIG. 1, numeral 9 designates a clutch plate attracted by the electromagnet 4 to the disc 5, and numeral 10 designates a driven shaft.
When the rolling bearing 3 shown in FIGS. 1 and 2 was used in a compressor unit between the electromagnetic clutch and compressor under a discharge pressure of 10-15 kg f/cm.sup.2 and suction pressure of 0.2-0.8 kg, grease leaked from the sealing portion 19 between the grease seal 15 and inner race 11. The leakage was realized even when organic thickner grease, which provides less leakage, was used.
More specifically, spaces A, B and C exist relative to the bearing 3. The space A is surrounded by heat transfer elements such as a compressor (not shown), the electromagnet 4, and the bearing 3 and is thus susceptible to increased heating. It has been found that the temperature distribution is such that the relative temperatures in spaces A, B and C can be expressed by the inequality A&gt;B&gt;C. The pressure is generated in the spaces A, B and C according to the relation A.gtoreq.B&gt;C. The air flow is thus directed from the space A in the clutch body 1 to which the compressor is attached, toward the space C between the clutch plate 9 and axial end of bearing 3 so that grease within the bearing 3 flows as shown in FIG. 2 during rotation with a component (h) in addition to flow components (a), (b). This component (h) brings the grease between seal 15 and the inner race 11 resulting in a grease leak.